PROJECT SUMMARY An effective blood stage Plasmodium falciparum malaria vaccine would be of immense global health benefit, particularly for infants and young children who suffer the greatest burden of malaria morbidity and mortality. Our limited knowledge of vaccine-induced and naturally acquired correlates of immune protection represents a major impediment to the development of such a vaccine. Elucidating B cell epitopes may provide information needed for vaccine development. A high-density peptide microarray would provide the means to examine both the breadth and depth of antigenic diversity and the role of this diversity in the development of protective immunity that we wish to emulate with a vaccine. Furthermore, finer precision than what is currently available, and correspondingly detailed epitope mapping, will be possible through the creation a densely overlapping peptide array with full coverage of the falciparum proteome, a so-called peptidome. We propose to study naturally acquired and vaccine-induced immunity to malaria with novel peptide microarrays of 16-mer peptide sequences with the overall goals of identifying peptides that correlate with protection and informing malaria vaccine development. We will use a new technology that has been used successfully for a human peptidome to study human seroreactivity to parasite-derived peptides for the first time. We will create two arrays: 1) A diversity array will contain short flexible peptides that represent malaria vaccine candidate antigens and their diverse variants based on sequencing of malaria parasites from the field; and 2) A peptidome array will encompass all P. falciparum peptides corresponding to a well- characterized reference strain. These two arrays will provide the means for both fine epitope mapping and identification of naturally acquired and vaccine-induced correlates of protection. The corresponding antigens will be worthy of further study as potential vaccines. Knowledge gained from this project will enable the ultra-dense peptide array to be used to study the humoral immune response to other infectious organisms.